The preparation of and the microstructures of glass/polymer alloys have been described in U.S. Pat. No. 5,043,369 (Bahn et al.). As explained therein, alloy articles consist essentially of an inorganic oxide glass, preferably a phosphate-based glass, and an organic thermoplastic or thermosetting polymer having a working temperature compatible with that of the glass. The low temperature phosphate glass is "melt mixed" with the polymer at the working temperature to form an intimate mixture; i.e., the glass and the polymer are both in a sufficiently fluid state to be blended together to yield a body exhibiting an essentially uniform, fine-grained microstructure.
Although the durability of the melt blends disclosed in the Bahn et al. patent was enormously better than that found in the prior art, those blends still exhibited some moisture corrosion, thus leading to changes in the constitution of the alloy body, including swelling and/or increased weight and volume, and to degradation in such alloy properties as reduced tensile, flexural, and impact strengths. Since it is very important that these alloys maintain their physical performance properties over an extended period of time, research was undertaken to discover methods for increasing the alloy's durability. Additionally, this search for increased durability was driven by both customer and industry demand for better and more durable materials.
It was surmised that increasing the durability might also open new application opportunities not currently contemplated for polymer-based materials, i.e., these glass/polymer alloys. The resultant more-durable alloy would be able to compete with glasses and ceramics as well.
In order to find a solution to increasing the durability, the mechanism of moisture corrosion was investigated. It was discovered that the weight and volume change commonly experienced with the subsequent reduction in properties was due, in part, to excess water incorporated by the alloys over and above that which could be attributed to the polymer fraction of the alloy. In other words, it was deduced that water was diffusing through the polymer and hydrating the phosphate glass phase.
There have been a number of references disclosed that have been directed towards methods of increasing the durability of phosphate glasses. For example, U.S. Pat. No. 4,079,022 (Ferrarini, Jr. et al.) discloses a glass composition comprising a relatively hydrophilic phosphate glass containing 50-72% mole percent P.sub.2 O.sub.5 and having formed upon its surface water-insoluble phosphate salts of metals selected from the group consisting of magnesium, calcium, barium, iron, aluminum, lead and zinc. Also described therein is a method for forming the insoluble surface coating which comprises exposing the glass to an alkaline solution, containing at least one of the above listed metal ions, for a time sufficient to form the relatively water-insoluble component on the surface of the glass. Because alloy processing conditions typically cause the destruction of the coating formed on the glass, this method of increasing the glass durability is not effective and cannot be used in the formation of the glass/polymer alloys. Specifically, the high forces generated by the high shear dispersive mixing needed to form the glass/polymer alloys destroy the water-insoluble phosphate salt coating described by Ferrarini, Jr. et al.